Energy generation and storage has long been a subject of study and development. Of special importance is the storage of electrical energy in a compact form which can be easily charged and discharged, such as the rechargeable battery and/or electrochemical capacitor. High power, particularly high current pulse, rechargeable electrochemical charge storage devices are very important in applications requiring electrical pulses, examples of which include digital communications devices, power tools, and portable computers. In each of these devices, high electrochemical kinetic rate, long cycle life of the electrode, low electrical resistivity, and good ionic conductivity of the electrolyte are extremely important.
Many high power electrochemical capacitor devices have been disclosed using ruthenium oxide as the electrochemically active material of one or both of the electrodes in an electrochemical capacitor device. Ruthenium oxide has the advantage of providing relatively long life and high power, though it is difficult to fabricate, and relatively expensive as compared to other capacitor materials. Thermally formed ruthenium oxide electrodes were developed in the 60's and 70's for the chlorine electrode employed in the chloro-alkali industry. One commonly used such electrode is disclosed in U.S. Pat. No. 3,632,498 to Beer, and entitled "ELECTRODE AND COATING THEREFOR." These electrodes were optimized for sodium chloride electrolysis. Generally speaking ruthenium oxide in such an application is a catalytic metal oxide and titanium oxide is a film forming oxide used in conjunction therewith. The Beer Patent claims that the film forming metal is higher than 50 mole percent of the materials of the coating, and specifically that the film forming metal is approximately 70 mole % while the catalytic metal oxide, i.e., TiO.sub.x is approximately 30 mole %.
While these types of electrode materials are known, they have not demonstrated satisfactory capacitance values in electrochemical capacitors. This is due to the fact that the ruthenium oxide content is too low to provide the high power required of most electrical device applications. Simply increasing the ruthenium oxide content in the electrodes does not resolve the problem since reduction of titanium oxide to below approximately 70 mole % will cause poor electrode adherence to the titanium substrates commonly used in such devices. Poor adherence of the electrode active material, results in poor cycle life, shorting, and in general poor device performance.
Accordingly, there exists a need for a dimensionally stable anode employing ruthenium oxide and titanium oxide in a manner sufficient to allow for good material adherence to a titanium substrate, without compromising the electrochemical performance of the ruthenium oxide in the material. Such an electrode should provide a good balance between device performance, costs, and overall process reliability.